1. Technical Field
The invention relates to precision measurement instruments, and to calipers with a movable jaw for measuring the dimensions of an object.
2. Description of the Related Art
Calipers utilize pairs of jaws for determining measurements. A first jaw is generally fixed at one end of a measurement scale while a second jaw is attached to a slider assembly that moves along the measurement scale. An outer dimension of an object may be measured by arranging the object between and against inner surfaces of the first and second jaws. An inner dimension of an object may be measured by arranging outer surfaces of the first and second jaws against the inner surfaces of the object (e.g., the walls of a hole). The slider assembly may be moved with a user's thumb.
For measuring the distance between the jaws of the caliper, electronic position encoders may be used, based on low-power inductive, position sensing technology for example. Such an encoder may comprise a readhead and a scale. The readhead may comprise a readhead sensor and readhead electronics. The readhead outputs signals that vary as a function of the position of the readhead sensor relative to the scale along a measuring axis. The scale may be affixed to an elongated scale member that includes a fixed first measuring jaw. The readhead is affixed to a slider assembly including the second measuring jaw, which is movable along the scale member. Measurements of the distance between the two measuring jaws may be determined based on the signals from the readhead.
Exemplary electronic calipers are disclosed in commonly assigned U.S. Pat. Nos. RE37490, 5,574,381, and 5,973,494, each of which is hereby incorporated by reference in its entirety. One deficiency in the use of prior calipers is that if the workpiece that is being measured is crooked or otherwise misaligned within the jaws of the caliper, then the desired outside measurement of the workpiece will likely be in error. A need exists for improving workpiece positioning alignment and/or repeatability in a caliper in an economical, ergonomically convenient, and intuitively understandable manner.